The long-term objective of the project is to accelerate research and discoveries in the areas of cancer, drug development, gene expression and therapy by (a) improving the imaging resolution, image quality, sensitivity and functionality, and (b) substantially lowering the cost of animal PET so more biology laboratories can afford this useful molecular imaging technology. Animal models, such as genetically engineered mice, have proven to be the tools of choice in these areas. These tools have even greater value when the biochemical and pharmaceutical processes are imaged and studied in vivo with PET. However, a rodent-PET with high resolution is too expensive to be within the reach of most biologists ($550,000-$750,000). Secondly, the imaging resolution should be improved further to probe smaller structures in mice, to detect smaller lesions and monitor smaller tumors. Thirdly, since inception, animal PET development has always been focusing solely on resolution at the expenses of detection sensitivity and cost. The compromise in sensitivity is mainly due to the high cost of its technology by resorting to decreasing the axial field of view (AFOV) to use fewer detectors. However, as resolution improves (smaller detector pixels but more pixels), the need for more counts (sensitivity) becomes more acute so as to maintain the same statistical quality per detector pixel. Hence, unless detection sensitivity is also improved, the full benefit of higher resolution cannot be realized. Furthermore, sensitivity is useful for probing lower levels of biochemical activities and to improve throughput. We propose to develop an animal PET at half the cost, while providing higher resolution than current commercial system, plus a 2.6-7 times higher sensitivity. It also has a 55% larger AFOV to increase throughput and to image the whole transgenic mouse in one bed position with more uniform image quality and to facilitate imaging wholebody dynamic changes in time. The large AFOV and ultrahigh resolution allow arterial input function to be imaged for quantifying tracer dynamics. This high performance low cost system is based on our low-cost PET detector design, novel efficient detector-production engineering technology, and electronic technology. The system also enable us to the study of a new 3-D data-acquisition and reconstruction method, whereby emission lines from all 4-pi-solid-angles can be acquired ("complete 3-D data"). This method may further improve image quality and the 3-D image reconstruction process.